Novel cytochrome p450 polypeptide with increased enzyme activity

ABSTRACT

The present invention pertains to an isolated P450 enzyme comprising or consisting of an amino acid sequence at least 80% identical to SEQ ID NO: 1, wherein said sequence comprises a threonine at position corresponding to position 225 and/or an aspartic acid mutation at position corresponding to position 289. The invention also concerns an isolated nucleic acid comprising a sequence encoding said enzyme, a vector comprising said nucleic acid, and a host cell containing said nucleic acid or said vector. Methods for preparing said enzyme and methods for producing steroid hormone precursors using the enzyme or the host cells featured in the invention are also provided.

The present invention concerns cytochrome P450 monooxygenases withincreased enzymatic activity.

Mammalian mitochondrial P450s constitute a small family of cytochromesthat perform specific reactions inside mitochondria and play animportant role in the metabolism of a variety of hydrophobic compounds.For example, P450c11beta and P450c11AS (encoded by the CYP11B1 andCYP11B2 genes) perform the final step of glucocorticoid andmineralocorticoid biosynthesis, respectively. P450c11beta is a classicalsteroid 11beta-hydroxylase that converts 11deoxycortisol intohydrocortisone, while P450c11AS catalyses the transformation ofdeoxycorticosterone into aldosterone in three consecutive steps. CYP27A1is another example of an inner mitochondrial P450 which is a sterol27-hydroxylase and vitamin D25 hydroxylase. Finally, the most emblematicmitochondrial P450 is P450scc (Side Chain Cleaving enzyme), encoded bythe CYP11A1 gene, which cleaves the cholesterol side chain thustransforming cholesterol into pregnenolone by two consecutivehydroxylations and a final cleaving. P450scc performs the first key stepof steroid biosynthesis by transforming a sterol into steroid.

The P450 ability to catalyze the regio-, chemo- and stereospecificoxidation of a vast number of substrates reflects their biological rolesand makes them important candidates for biotechnological applications.Particularly, steroid hormones are widely used as anti-inflammatory,contraceptive and antiproliferative drugs. In mammals, the synthesis ofthese steroids starts with the side-chain cleaving reaction ofcholesterol to pregnenolone. Pregnenolone serves as a basis for theproduction of further steroid hormones such as hydrocortisone and greatinterests are associated with its industrial large scale conversion fromlow-priced substrates such as cholesterol and its plant-derivedanalogues. However, side-chain cleaving reaction of cholesterol topregnenolone is a limiting step in steroids overall process. In mammals,it is catalyzed by the membrane-bound CYP11A1 enzyme.

However, for multiple reasons, biotechnological and industrial use ofthe P450s is difficult to implement and is not satisfactory.Mitochondrial P450 use a specific chain of electron transporters made oftwo proteins, namely ferredoxin reductase (FdxR) and ferredoxin (Fdx1),also named adrenodoxin reductase (AdR) and adrenodoxin (Adx). In thenatural situation in vivo, FdxR gains electron from NADPH and Fdx1shuttles electron from FdxR to the mitochondrial P450. An in vitrosystem has been developed where FdxR is at a catalytic concentration(0.5 μM) and Fdx1 at a saturation concentration (10 μM). In order forthis in vitro system to be efficient, electrons must be appropriatelyfluxed to the P450.

To try to overcome these difficulties, some authors fused the threepeptides P450scc (or P450c11beta), Fdx1 and FdxR using variable hinge orlinker sequences. Even if this triple fusion results in a functionalprotein, its efficacy is low compared to the “bona fide” polypeptide andit cannot be used at industrial scale. Moreover, the mitochondrialenvironment is difficult to mimic in a microbial recombinant system. Forexample, the P450scc polypeptide can be properly targeted to yeastmitochondria. However, the targeted polypeptide cannot convert sterolinto pregnenolone due to absence of substrate in the mitochondria and/orto improper folding or targeting of P450scc.

Different recombinant systems are used to produce biosyntheticpregnenolone from plant sterol. For instance, a biosynthesis system wasdeveloped in the yeast Saccharomyces cerevisiae. In this system, P450sccis targeted outside the mitochondria at the plasma membrane togetherwith FdxR and Fdx1, and the sterol pathway is routed to produce sterolat the membrane. Also, P450c11beta may be targeted to mitochondriatogether with Fdx and FdxR1 where it may convert 11-deoxycortisol intocortisol. A bioconversion system was developed in Bacillus megaterium.In this system, cholesterol can be converted into pregnenolone by matureforms of P450scc, Fdx1 and FdxR1. Biosynthesis remains the mostattractive technology at the industrial scale since the substrate ismade as a soluble molecule from a simple carbon source by the hosttherefore avoiding the burden of using detergents.

Recently, efforts have been made to produce new P450scc polypeptideswith improved properties. For instance, a recombinant P450scc mutantbearing a K193E mutation was created. This mutant is more soluble andthus less prone to aggregation than the recombinant wild-typepolypeptide. Therefore, a higher expression level is obtained with thismutant without changing its enzymatic characteristics. However, there isstill a need for improved P450scc polypeptides with increased enzymaticactivity allowing optimized production of steroid hormones, particularlysuitable for industrial processes.

The inventors have developed a new P450scc polypeptide bearing specificmutations. This mutant shows unexpectedly an improved enzymatic activityin terms of substrate conversion into steroid hormones.

The present invention thus concerns a new isolated P450 enzymecomprising or consisting of an amino acid sequence at least 80%identical to SEQ ID NO: 1, wherein said sequence comprises a threonineat position corresponding to position 225 and/or an aspartic acidmutation at position corresponding to position 289. In some embodiments,the new P450 enzyme is at least 85%, 90%, 95%, 98% or 99% identical toSEQ ID NO:1.

The invention also concerns an isolated nucleic acid which comprises orconsists of a nucleotide sequence encoding said enzyme, a vectorcomprising said nucleic acid which is operatively associated withexpression control sequences, and a host cell containing said nucleicacid or said vector, said host cell being, for example, a microorganism.

In one embodiment, the invention provides a genetically engineeredmicroorganism capable of converting a substrate into a steroid hormoneprecursor. The substrate can be, for example, a polycyclic, unsaturatedmono alcohol having an aliphatic side chain, such as cholesterol, acholesterol analogue or a cholesterol derivative. The geneticallyengineered microorganism comprises, for example, a nucleic acid encodinga new P450 enzyme featured in the invention, and optionally a nucleicacid sequence encoding an adrenodoxin (Adx) and/or a nucleic acidsequence encoding an adrenodoxin reductase (AdR).

In another aspect, the invention provides an in vitro method forpreparing a P450 enzyme featured in the invention, said methodcomprising the steps of:

a) culturing a host cell under conditions suitable to obtain expressionof the P450 enzyme; and

b) recovering the expressed enzyme.

In another embodiment, a P450 enzyme featured in the invention is usedfor producing a steroid hormone precursor.

The invention further relates to a method for producing a steroidhormone precursor, comprising the steps of:

a) providing a microorganism expressing a P450 enzyme featured in theinvention,

b) culturing said microorganism under conditions allowing the expressionof the P450 enzyme,

c) contacting the microorganism culture obtained at step b) with asubstrate selected from the group consisting of polycyclic andunsaturated mono alcohols having an aliphatic side chain such ascholesterol, a cholesterol analogue and a cholesterol derivative, inconditions allowing the production, by the microorganism, of a steroidhormone precursor from said substrate, and

d) recovering the steroid hormone precursor produced.

The invention also pertains to a method, such as an in vitro method, forproducing a steroid hormone precursor, comprising the steps of:

a) contacting a P450 enzyme featured in the invention with an isolatedadrenodoxin (Adx) polypeptide, an isolated adrenodoxin reductase (AdR)polypeptide and a substrate selected from the group consisting ofpolycyclic and unsaturated mono alcohols having an aliphatic side chainsuch as cholesterol, cholesterol analogues and derivatives in conditionsallowing the transformation of said substrate into a steroid hormoneprecursor, and

b) recovering the steroid hormone precursor obtained.

Steroid hormones are widely used as anti-inflammatory, contraceptive andantiproliferative drugs. The invention is of utility to produce asteroid hormone precursor and aid the synthesis of steroid hormones foruse in humans. Steroid hormone precursor, such as pregnelonone, servesas a basis for the production of further steroid hormones such ashydrocortisone and great interests are associated with its industriallarge scale conversion.

DESCRIPTION OF THE INVENTION

Enzymes

By an “isolated” enzyme or polypeptide, it is intended that the enzymeor polypeptide is no longer in its natural environment within theorganism in which it is originally expressed. When referring to anenzyme or polypeptide, “purified” means that the indicated molecule ispresent in the substantial absence of other biological macromolecules ofthe same type. The term “purified” as used herein means at least 75% byweight, at least 85% by weight, at least 95% by weight, or at least 98%by weight, of biological macromolecules of the same type are present.

The term “cytochrome P450 enzyme” or “P450 enzyme” refers to amonooxygenase which is capable of catalyzing certain reactions such asthose reviewed in Van Bogaert et al, 2011, FEBS J. 278(2): 206-221 or inUrlacher and Girhard, 2011, Trends in Biotechnology 30(1): 26-36, or atthe website dmelson.uthsc.edu/CytochromeP450.html. As an example of sucha wild-type P450 enzyme, the sequence SEQ ID NO: 4 represents the matureform of Bos taurus CYP11A1. The complete sequence of Bos taurus CYP11A1including a transit peptide is referenced as P00189 inUniProtKB/Swiss-Prot database (last sequence update: Jul. 21, 1986).

The cytochrome P450 enzymes featured in the invention may bemembrane-bound (insoluble) or cytoplasmic (soluble) in their respectiveoriginal hosts. For example, P450scc (SEQ ID NO:4) catalyzes theside-chain cleavage reaction of polycyclic and unsaturated mono alcoholshaving an aliphatic side chain such as cholesterol, cholesterolanalogues and derivatives thereof into pregnenolone or other steroidhormone precursors and derivatives, as a non-limiting example.

The inventors have developed a new P450 enzyme of sequence SEQ ID NO: 1with improved enzymatic activity. In comparison with SEQ ID NO: 4(wild-type scc enzyme with R at position 225 and N at position 289), theamino acid sequence SEQ ID NO: 1 comprises two mutations: an arginine tothreonine mutation at position corresponding to position 225 of thesequence SEQ ID NO: 4 and an asparagine to aspartic acid mutation atposition corresponding to position 289 of the sequence SEQ ID NO: 4.

In a specific embodiment, the new P450 enzyme featured in the inventiondisplays a monooxygenase activity catalyzing the transformation ofcholesterol into pregnenolone. In a particular embodiment, the new P450enzyme displays at least 80% or more, in particular at least 85%, 90%,95%, 100%, 125%, 150%, 175%, 200%, 225%, 250%, 275%, more particularlyat least 300% or more of the monooxygenase activity of the P450 enzymeof sequence SEQ ID NO: 4.

The isolated P450 enzyme featured in the invention comprises or consistsof an amino acid sequence at least 80% identical to SEQ ID NO: 1,wherein said sequence comprises a threonine at position corresponding toposition 225 and/or an aspartic acid at position corresponding toposition 289. In some embodiments, the new P450 enzyme is at least 85%,90%, 95%, 98% or 99% identical to SEQ ID NO:1.

Variations in amino acid sequence may be introduced by substitution,deletion or insertion of one or more codons into the nucleic acidsequence encoding the enzyme that results in a change in the amino acidsequence of the enzyme. Amino acid substitutions may be conservative ornon-conservative. In some embodiments, substitutions are conservativesubstitutions, in which one amino acid is substituted for another aminoacid with similar structural and/or chemical properties.

A “conservative amino acid substitution” is one in which an amino acidresidue is substituted by another amino acid residue having a side chainR group with similar chemical properties (e.g., charge orhydrophobicity). In general, a conservative amino acid substitution willnot substantially change the functional properties of a protein.Examples of groups of amino acids that have side chains with similarchemical properties include 1) aliphatic side chains: glycine, alanine,valine, leucine, and isoleucine; 2) aliphatic-hydroxyl side chains:serine and threonine; 3) amide-containing side chains: asparagine andglutamine; 4) aromatic side chains: phenylalanine, tyrosine, andtryptophan; 5) basic side chains: lysine, arginine, and histidine; 6)acidic side chains: aspartic acid and glutamic acid; and 7)sulfur-containing side chains: cysteine and methionine. Conservativeamino acid substitution groups are: valine-leucine-isoleucine,phenylalanine-tyrosine, lysine-arginine, alanine-valine,glutamate-aspartate, and asparagine-glutamine.

For example, an amino acid sequence at least 80% identical to SEQ ID NO:1 may be a polypeptide having at least one substitution at a particularamino acid residue. In some embodiments, an amino acid sequence at least80% identical to SEQ ID NO: 1 has at least about 80%, 81%, 82%, 83%,84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%,98%, 99% amino acid sequence identity to the sequence SEQ ID NO: 1.Amino acid sequence identity is defined as the percentage of amino acidresidues in the sequence at least 80% identical to SEQ ID NO: 1 that areidentical with the amino acid residues in the reference sequence SEQ IDNO: 1, after aligning the sequences and introducing gaps, if necessary,to achieve the maximum percentage of sequence identity, and notconsidering any conservative substitutions as part of the sequenceidentity. Sequence identity may be determined over the full length ofthe at least 80% identical sequence, the full length of the referencesequence, or both. The percentage of identity for amino acid sequencesmay be calculated by performing a pairwise global alignment based on theNeedleman-Wunsch alignment algorithm to find the optimum alignment(including gaps) of two sequences along their entire length, forinstance using Needle, and using the BLOSUM62 matrix with a gap openingpenalty of 10 and a gap extension penalty of 0.5.

In the P450 enzyme comprising or consisting of an amino acid sequence atleast 80% identical to SEQ ID NO: 1, the amino acid modifications ascompared with SEQ ID NO: 1 are typically located at positions such thatthey do not significantly undermine the biological activity of theenzyme. Indeed, the cytochrome P450 amino acid sequence presenting atleast 80% identical to SEQ ID NO: 1 exhibits at least the samebiological activity as the polypeptide of sequence SEQ ID NO: 1.

A “same biological activity” may denote a same biological function.Therefore, a polypeptide having a same biological activity as thepolypeptide of sequence SEQ ID NO: 1 may for instance be a polypeptidehaving monooxygenase activity. Techniques to determine the monooxygenaseactivity of an enzyme are well known from the skilled person. Forinstance, a polypeptide having a same biological activity as thepolypeptide of sequence SEQ ID NO: 1 may be a polypeptide able tocatalyse the side-chain cleavage reaction of polycyclic and unsaturatedmono alcohols having an aliphatic side chain such as cholesterol,cholesterol analogues and derivatives to pregnenolone or other steroidhormone precursors and derivatives, as a non-limiting example. In thiscase, the catalysing activity of a compound can easily be evaluated invitro (as shown in Woods, S. T., J. Sadleir, et al. (1998) “Expressionof catalytically active human cytochrome p450scc in Escherichia coli andmutagenesis of isoleucine-462.”; Arch Biochem Biophys 353(1): 109-15) orin vivo (as shown in Duport, C., R. Spagnoli, et al. (1998)“Self-sufficient biosynthesis of pregnenolone and progesterone inengineered yeast”; Nat Biotechnol 16(2): 186-9) by the person skilled inthe art, for example by means of the protocol described in Example 1.

Typically, catalysing activity may be tested in an in vitro conversionassay wherein 150 mM of HEPES buffer, adjusted to pH 7.4, containing0.05% Tween-20 and 1 mM MgCl2, may be applied as reaction buffer. 1 unitof glucose-6-phosphate dehydrogenase, with 5 mM glucose-6-phosphate assubstrate, may serve as a NADPH-regenerating system. Typically, theconcentrations of CYP11A1, Adx and AdR may be of 1 μM, 20 μM and 0.5 μM,or of 0.25 μM, 5 μM and 0.125 μM, respectively. 20 μM of cholesterol,dissolved in 45% 2-hydroxypropyl-β-cyclodextrin, may serve as substratefor CYP11A1. Typically, the samples are pre-warmed to 37° C. and thereaction was started by addition of NADPH to a final concentration of100 μM. The mixtures may be incubated at 37° C. with agitation for 30 s.The reaction may be stopped by boiling the samples in water for 30 s. Toallow photometric detection at 240 nm, the steroids may be convertedinto their 3-keto-Δ4 derivatives using a cholesterol oxidase fromNocardia spec. Typically, 20 μl of a cholesterol oxidase solution (5 mgcholesterol oxidase and 5 mg Na-cholate dissolved in 5 ml of 50 mM HEPESbuffer pH 7, containing 0.05% Tween-20) is added to the samples. Afterincubation at 37° C. for 1 h, 11-deoxycorticosterone (DOC) may be addedto the reaction mixtures as an internal standard, followed by a 2-timesextraction with equal volumes of ethylacetate. After evaporation, theextracts may be dissolved in acetonitrile/water.

Catalysing activity may also be tested in an in vivo conversion assaywherein the conversion of 300 μM cholesterol into progesterone istypically evaluated by HPLC after 24 h. Bacillus megaterium may becultivated in TB-medium containing 10 μg/ml tetracycline at 37° C. with180 rpm shaking. Protein expression may be induced by adding 0.25 g ofxylose dissolved in 1 mL water, followed by the subsequent addition ofthe substrate, dissolved in 2-hydroxypropyl-β-cyclodextrin.

Alignment of the sequence SEQ ID NO: 1 with an amino acid sequence atleast 80% identical to SEQ ID NO: 1 may be performed. As these twosequences have a high percentage of identity, most of their amino acidsare identical. Therefore, amino acid numbering may be defined for bothsequences in such a way that at least 80% of the amino acids present atpositions bearing the same number in both sequences are identical (byintroducing gaps, if necessary, to achieve the maximum percentage ofsequence identity). In this context, “a position corresponding toposition X” of the sequence SEQ ID NO: 1 denotes the position bearingsaid number X in the sequence at least 80% identical to SEQ ID NO: 1.The sequence SEQ ID NO: 1 may therefore be taken as a “referencesequence” for the numbering of amino acid positions in an alignment withan amino acid sequence at least 80% identical to SEQ ID NO: 1, in such away that at least 80% of the amino acids present at a “correspondingposition” in both aligned sequences are identical.

In one embodiment, the isolated P450 enzyme featured in the inventioncomprises or consists of an amino acid sequence at least 80% identicalto SEQ ID NO: 1, wherein said sequence comprises both a threonine atposition corresponding to position 225 and an aspartic acid at positioncorresponding to position 289.

In another embodiment, the P450 enzyme featured in the inventioncomprises or consists of a sequence selected from the group consistingof SEQ ID NO: 1, SEQ ID NO: 2 and SEQ ID NO: 3.

In still another embodiment, the P450 enzyme featured in the inventionconsists of the sequence SEQ ID NO: 1.

The enzyme featured in the invention may include one or more tag(s),which may facilitate its purification. For example, the tag can be apoly-histidine (poly-His) tag.

Nucleic Acids, Vectors, Host Cells and Method of Producing the Enzyme

In one embodiment, the invention features an isolated nucleic acid whichcomprises or consists of a sequence encoding a P450 enzyme featured inthe invention.

Isolated nucleic acids featured in the invention, also calledpolynucleotides, may be DNA or RNA molecules, that encode the P450enzyme defined in the section “Enzymes”, while taking into account thedegeneracy of the genetic code. The isolated nucleic acids can beobtained by standard techniques well known by those skilled in the art,such as by in vitro DNA amplification or polymerisation, in vitro genesynthesis, oligonucleotide ligation, or by a combination of thesetechniques.

The nucleic acids featured in the invention are advantageously inisolated or purified form. The terms “purified” and “isolated” have thesame meaning as defined above.

As will be understood by those of skill in the art, it may beadvantageous in some instances to produce polypeptide-encodingnucleotide molecules possessing codons non-naturally occurring in thenatural nucleotide molecule. For example, codons preferred by aparticular prokaryotic or eukaryotic host can be selected to increasethe rate of recombinant polypeptide expression.

A nucleic acid featured in this invention can also include sequencesencoding tags, carrier proteins, signal peptides, or non-transcribed ortranslated sequences increasing expression or stability of the molecule.

The nucleic acids featured in the invention may be used to produce arecombinant P450 enzyme in a suitable expression system. The term“expression system” means a host cell and compatible vector undersuitable conditions, e.g. for the expression of a protein encoded by aforeign nucleic acid carried by the vector and introduced to the hostcell.

Typically, the nucleic acid may be included in any suitable vector.

Thus, in some embodiments, the invention features a vector comprising anucleic acid as defined above operatively associated with expressioncontrol elements, and a host cell containing said nucleic acid or saidvector.

The terms “vector”, “cloning vector” and “expression vector” mean thevehicle by which a DNA or RNA sequence (e.g. a foreign gene) can beintroduced into a host cell, so as to transform the host and promoteexpression (e.g. transcription and translation) of the introducedsequence.

Any expression vector can be used, such as a plasmid, cosmid, episome,artificial chromosome, phage or a viral vector. Examples of plasmidsinclude replicating plasmids comprising an origin of replication, orintegrative plasmids, such as for instance pUC, pcDNA, pBR, and thelike.

Other examples of vectors include vectors for animal cells such aspAGE107 (Miyaji H et al. 1990), pAGE103 (Mizukami T et al. 1987),pHSG274 (Brady G et al. 1984), pKCR (O'Hare K et al. 1981), pSG1 betad2-4-(Miyaji H et al. 1990) and the like.

Examples of viral vectors include adenoviral, retroviral, herpes virusand AAV vectors. Recombinant viruses may be produced by techniques knownin the art, such as by transfecting packaging cells or by transienttransfection with helper plasmids or viruses. Typical examples of viruspackaging cells include PA317 cells, PsiCRIP cells, GPenv+ cells, 293cells, etc. Detailed protocols for producing such replication-defectiverecombinant viruses may be found for instance in WO 95/14785, WO96/22378, U.S. Pat. No. 5,882,877, U.S. Pat. No. 6,013,516, U.S. Pat.No. 4,861,719, U.S. Pat. No. 5,278,056 and WO 94/19478.

The expression vector may comprise a functional expression cassette,such as anexpression cassette comprising a nucleic acid sequenceencoding a polypeptide featured in the invention, which is operablylinked to expression control sequences.

“Expression control sequence(s)” refers to element(s) necessary forexpression of a polypeptide and, optionally, for its regulation.Expression control sequence(s) may for instance include a promotersequence, signals for initiation and termination of translation, as wellas appropriate regions for regulation of translation, such as apromoter, enhancer, terminator and the like, to cause or directexpression of said polypeptide.

In one embodiment, a vector featured in the invention may also comprisea marker gene, for example a gene making it possible to select between atransformed organism and an organism which does not contain thetransfected foreign DNA. A marker gene may be a gene that confersresistance to an antibiotic.

According to a specific embodiment, a vector featured in the inventionmay further comprise a nucleic acid sequence encoding an adrenodoxin(Adx) and/or a nucleic acid sequence encoding an adrenodoxin reductase(AdR). Adx and AdR are oxydo-reduction partners of P450 enzymes.

“AdR” refers to Adrenodoxin reductase (EC: 1.18.1.6) orAdrenodoxin-NADP+ reductase, the enzyme which is known as the firstcomponent in the mitochondrial Cytochrome P450 electron transfer systemand which is involved in the biosynthesis of all steroid hormones.

In a specific embodiment, said AdR enzyme is selected from the groupconsisting of

AR (NADPH:adrenodoxin oxidoreductase (EC=1.18.1.6) encoded by arh1 gene)from Schizosaccharomyces pombe or from Saccharomyces cerevisiae and FNR(Ferredoxin-NADP reductase (EC=1.18.1.2) encoded by fpr gene) fromEscherichia coli.

In a specific embodiment, the AdR enzyme is AdR from Bos taurus(referenced as P08165 in UniProtKB/Swiss-Prot, last sequence update:Jul. 15, 1998). In another specific embodiment, the protein sequence ofsaid AdR is SEQ ID NO: 7. In another specific embodiment, the proteinsequence of said AdR is a variant of SEQ ID NO: 7, provided it retainsits biological activity.

By “Adx” is meant Adrenodoxin or Ferredoxin 1, the protein which isknown for its activity of transferring electrons from Adrenodoxinreductase toCYP11A1.

In a specific embodiment, said Adx protein is selected from the groupconsisting of Fdx from mammalian origin, Etp1fd from Schizosaccharomycespombe and Yah1 from Saccharomyces cerevisiae.

In a specific embodiment, the Adx protein is Adx from Bos taurus(referenced as P00257 in UniProtKB/Swiss-Prot, last sequence update:Jul. 1, 1989). In another specific embodiment, the protein sequence ofsaid Adx is SEQ ID NO: 8. In another specific embodiment, the proteinsequence of said Adx is a variant of SEQ ID NO: 8, provided it retainsits biological activity.

A vector or nucleic acid featured in the invention can be used totransform host cells according to techniques commonly known to thoseskilled in the art. Insertion of said vector into the host cell may betransient or stable.

The vector may also contain sequences encoding specific signals whichtrigger the secretion of the translated protein or its targeting tocellular compartments or organelles. These various control signals areselected according to the host cell and may be inserted into vectorswhich self-replicate in the host cell, or into vectors which integratethe genome of said host.

Host cells may be prokaryotic or eukaryotic, including but not limitedto bacteria, yeasts, plant cells, animal cells, insect cells, andmammalian cells, including cell lines which are commercially availablein some embodiments, the expression host cells are Escherichia coli,Lactobacilli, Bacillus, in particular Bacillus megaterium, probioticbacteria, Pichia pastoris, Saccharomyces cerevisiae, insect cells, plantcells, COS cells and CHO cells. In one embodiment, the host cell is aprokaryotic cell, in particular a bacterial cell. In another particularembodiment, the host cell is a eukaryotic cell, such as a yeast cellsuch as a cell of Saccharomyces cerevisiae.

Common expression systems include bacterial host cells and plasmidvectors, insect host cells and Baculovirus vectors, and mammalian hostcells and vectors. Specific examples include E. coli, B. megaterium,Kluyveromyces or Saccharomyces yeasts, mammalian cell lines (e.g., Verocells, CHO cells, 3T3 cells, COS cells, etc.) as well as primary orestablished mammalian cell cultures (e.g., produced from lymphoblasts,fibroblasts, embryonic cells, epithelial cells, nervous cells,adipocytes, etc.). Examples also include mouse SP2/0-Ag14 cells (ATCCCRL1581), mouse P3X63-Ag8.653 cells (ATCC CRL1580), CHO cells in which adihydrofolate reductase gene (also referred to as “DHFR gene”) isdefective (Urlaub G et al; 1980), rat YB2/3HL.P2.G11.16Ag.20 cells (ATCCCRL1662, also referred to as “YB2/0 cell”), and the like.

In another embodiment, the invention features a cell which has beentransfected, infected or transformed by a nucleic acid and/or a vectorprovided herein. Consequently, the present invention further concerns ahost cell containing a nucleic acid and/or a vector described herein, aswell as progeny and/or derivatives of such host cells. In oneembodiment, the host cell is a genetically engineered microorganism.

As used herein, the “microorganism” can be an Escherichia coli, Bacilluslicheniformis, Bacillus megaterium, Bacillus subtilis, Kluyveromyceslactis, Saccharomyces cerevisiae or Schizosaccharomyces pombe.

As shown in Woods, S. T., J. Sadleir, et al. (1998) (Expression ofcatalytically active human cytochrome p450scc in Escherichia coli andmutagenesis of isoleucine-462. Arch Biochem Biophys 353(1): 109-15), themature form of human P450scc was expressed in Escherichia coli in orderto provide a more convenient source of the human enzyme and to enablestructure-function studies to be done using site-directed mutagenesis.This expression system enabled to produce larger quantities of activecytochrome than have previously been isolated from placentalmitochondria. The expressed P450scc was purified to near homogeneity andshown to have catalytic properties comparable to the enzyme purifiedfrom the human placenta. The mature form of human adrenodoxin was alsoexpressed in E. coli and supported cholesterol side chain cleavageactivity with the same Vmax as that observed using bovine adrenodoxinbut with a higher Km. Mutation of Ile-462 to Leu in human P450scc causeda decrease in the catalytic rate constant (kcat) with cholesterol assubstrate, increased the Km for 22R-hydroxycholesterol, but did notaffect the kinetic constants for 20 alpha-hydroxycholesterol.

As shown in Duport, C., R. Spagnoli, et al. (1998) (Self-sufficientbiosynthesis of pregnenolone and progesterone in engineered yeast. NatBiotechnol 16(2): 186-9), the first two steps of the steroidogenicpathway were reproduced in Saccharomyces cerevisiae. Engineering ofsterol biosynthesis by disruption of the delta 22-desaturase gene andintroduction of the Arabidopsis thaliana delta 7-reductase activity andcoexpression of bovine side chain cleavage cytochrome P450, adrenodoxin,and adrenodoxin reductase, lead to pregnenolone biosynthesis from asimple carbon source. Following additional coexpression of human 3 beta-hydroxysteroid dehydrogenase/isomerase, pregnenolone was furthermetabolized to progesterone. Steroid formation appeared to be coupled toyeast sterol biosynthesis.

In Szczebara, F. M., C. Chandelier, et al. (2003) (Total biosynthesis ofhydrocortisone from a simple carbon source in yeast; Nat Biotechnol21(2): 143-9), the production of hydrocortisone, the major adrenalglucocorticoid of mammals and an important intermediate of steroidaldrug synthesis, was reported from a simple carbon source by recombinantSaccharomyces cerevisiae strains. An artificial and fullyself-sufficient biosynthetic pathway involving 13 engineered genes wasassembled and expressed in a single yeast strain. Endogenous sterolbiosynthesis was rerouted to produce compatible sterols to serve assubstrates for the heterologous part of the pathway. Biosynthesisinvolved eight mammalian proteins (mature forms of CYP11A1, adrenodoxin(ADX), and adrenodoxin reductase (ADR); mitochondrial forms of ADX andCYP11B1; 3beta-HSD, CYP17A1, and CYP21A1). Optimization involvedmodulating the two mitochondrial systems and disrupting of unwanted sidereactions associated with ATF2, GCY1, and YPR1 gene products.Hydrocortisone was the major steroid produced. This work demonstratedthe feasibility of transfering a complex biosynthetic pathway fromhigher eukaryotes into microorganisms.

In a specific embodiment, the microorganism is Bacillus megaterium, inparticular the strain referred to as Bacillus megaterium MS941. Theexpression “Bacillus megaterium MS941 strain” refers to the strainreferenced in Wittchen and Meinhardt, 1995, Appl Microbiol Biotechnol.42: 871-877, and derived from the DSM319 strain (Deutsche Stammsammlungvon Mikroorganismen and Zellkulturen).

The system described previously using E Coli and the system using B.megaterium are two systems that are capable of realizing sterol andsterol derivatives conversion either in vitro with E. coli or in cellulowith B. megaterium. These technologies can evaluate the capacities ofP450scc and substrates to function together. Both technologies requirean efficient method to solubilize the substrates so that they areaccessible to the enzyme. This solubilization could be challenging atthe industrial level (large voume) both in financial and scientificterms.

A third organism S. cerevisiae is a particularly advantageous organismin this regard; its large fermentation is well mastered at cubic meteror higher levels and it has the potent capacity to produce steroids suchas pregnenolone from a simple carbon source such as glucose and/orethanol thus avoiding of detergent or solubilizing chemical such asbeta-cyclodextrin (as referenced above: Duport, C., R. Spagnoli, et al.(1998); Szczebara, F. M., C. Chandelier, et al. (2003)). To permit invivo steroid synthesis, the sterol biosynthesis was routed to produce aP450scc compatible sterol.

As S. cerevisiae fermentation is well mastered at large scale,introduction of the newly described P450scc cDNA into a suitable S.cerevisiae routed for campesterol, or other sterols described assubstrates, in the presence of an appropriate electron carrier is anasset for production of steroid. This recombinant organism can be usedfor evaluating a new P450scc cDNA as described herein.

Therefore, in another specific embodiment, the microorganism isSaccharomyces cerevisiae.

The term “genetically engineered” microorganism refers to anymicroorganism which has been modified by genetic engineering techniquesknown in the field by the skilled in the art. For methods related toparticular microorganisms, the person skilled in the art can refertoreference manuals such as for yeast: “Methods in yeast genetics” —Alaboratory course manual by M Rose, F Winston and P Hieter. pp 198. ColdSpring Harbor Laboratory Press, Cold Spring Harbor, N.Y. 1990. ISBN0-87969-354-1.

These techniques are conventional techniques, unless otherwiseindicated, in the fields of bioinformatics, cell biology, cell culture,molecular biology, transgenic biology, microbiology, recombinant DNA,and immunology, which are within the skill of the art. Such techniquesare explained fully in the literature.

As used herein, “genetic engineering techniques” relate to technologiesallowing the expression or overexpression of gene expression known inthe field by the skilled in the art. The expression or overexpression ofa gene of interest can be achieved by introducing into a cell or amicroorganism an exogenous nucleic acid sequence comprising such gene ofinterest, by any transformation technologies known by the skilled in theart.

The term “transformation” or “transfection” means the introduction of a“foreign” (i.e. heterologous) gene, DNA or RNA sequence to a host cell,so that the host cell will express the introduced gene or sequence toproduce a desired substance, typically a protein or enzyme coded by theintroduced gene or sequence. The transfection of the host cell may beperformed using any standard technique, such as chemical transformation,electroporation, phosphate calcium precipitation or lipofection. Thetransformation techniques also include for instance the PEG-mediatedprotoplast transformation technique (Barg et al, 2005, MicrobialProcesses and Products 165-184).

“Exogenous nucleic acid sequence(s)” relates to nucleic acid sequence(s)non originally and/or non naturally expressed in the consideredmicroorganism or the way it is in the natural strain of microorganism(in term of expression level for example), and which have been used totransform said microorganism in order to obtain a genetically engineeredmicroorganism as referred above. In a specific embodiment, the exogenousnucleic acid sequence originates from another species than theconsidered microorganism (e.g. another species of microorganism ororganism). In another specific embodiment, exogenous sequence originatesfrom the same microorganism.

Said exogenous nucleic acid sequence(s) may encode proteins of interestsuch as cytochrome P450 and oxydo-reduction partners AdR and Adx and theexpression “exogenous DNA” can designate each individual sequence orencompass a whole sequence comprising each individual sequence. As anon-limiting example, said exogenous nucleic acid sequences areintegrated into the genome of said microorganism by techniques known inthe field, such as by homologous recombination.

In one aspect, the invention provides a genetically engineeredmicroorganism capable of converting a substrate selected from the groupconsisting of polycyclic and unsaturated mono alcohols having analiphatic side chain such as cholesterol, cholesterol analogues andderivatives into a steroid hormone precursor, wherein said microorganismcomprises a nucleic acid featured in the invention, and optionally anexogenous nucleic acid sequence encoding an Adx and/or an exogenousnucleic acid sequence encoding an AdR.

In a specific embodiment, the genetically engineered microorganism isSaccharomyces cerevisiae.

In another specific embodiment, the genetically engineered microorganismis Bacillus megaterium, in particular the Bacillus megaterium MS941strain.

The present invention also relates to an in vitro method for preparing aP450 enzyme featured in the invention, said method comprising the stepsof:

a) culturing a host cell under conditions suitable to obtain expressionof the P450 enzyme; and

b) recovering the expressed enzyme.

“Conditions suitable to obtain expression of the P450 enzyme” are wellknown by the skilled in the art. Typically, either LB-(25 g/L), TB-(24g/L yeast extract, 12 g/L tryptone, 0.4% glycerol, 10 mM potassiumphosphate buffer) or EnPresso™ Tablet medium are used for thecultivation of the host cell. A pre-culture may be performed byinoculating 50 mL medium containing 10 μg/mL tetracycline with cellsfrom a plate or glycerol stock. A main culture may then be performed byinoculating 50 mL medium containing 10 μg/mL tetracycline with 500 μLsample of the pre-culture. The main culture is typically grown until anoptical density of ˜0.4 is reached. Protein expression may be inducedafter addition of 0.25 g xylose dissolved in 1 mL distilled water.

The P450 enzyme can then be purified by means of well-known proceduresfor purification: it may be purified from lysates or cell extracts,inclusion bodies or from the culture supernatant by methods such as HPLCchromatography, immunoaffinity techniques with specific antibodies, andthe like.

Alternatively, the P450 enzyme may be expressed in vitro with acell-free transcription and translation system from a DNA or RNA matrixcontaining required elements for its expression in a cell lysate orreconstituted system (for example, Rapid Translation System®, RocheDiagnostics or Retic Lysate IVT™, Ambion).

Methods of Producing Steroid Hormone Precursor

As shown in Examples 2-4, the inventors have developed a new P450sccenzyme bearing specific mutations which shows an improved enzymaticactivity in terms of substrate conversion into steroid hormoneprecursor.

Therefore, in another aspect, the invention pertains to the use of aP450 enzyme featured in the invention for producing a steroid hormoneprecursor.

The invention further provides methods for producing a steroid hormoneprecursor as described below.

A first method for producing a steroid hormone precursor comprises thesteps of:

a) providing a microorganism as described above,

b) culturing said microorganism under conditions allowing the expressionof a P450 enzyme featured in the invention,

c) contacting the microorganism culture obtained at step b) with asubstrate selected from the group consisting of polycyclic andunsaturated mono alcohols having an aliphatic side chain such ascholesterol, a cholesterol analogue and a cholesterol derivative, inconditions allowing the production, by the microorganism, of a steroidhormone precursor from said substrate, and

d) recovering the steroid hormone precursor produced.

According to a specific embodiment, steps b) and c) are performedsimultaneously. In this case, the method for producing a steroid hormoneprecursor comprises the steps of:

a) providing a microorganism as described above,

b) culturing said microorganism in the presence of a substrate selectedfrom the group consisting of polycyclic and unsaturated mono alcoholshaving an aliphatic side chain such as cholesterol, a cholesterolanalogue and a cholesterol derivative, in conditions allowing theexpression of a P450 enzyme featured in the invention and allowing theproduction, by the microorganism, of the steroid hormone precursor fromsaid substrate, and

c) recovering the steroid hormone precursor produced.

A second method for producing a steroid hormone precursor comprises thesteps of:

a) contacting a P450 enzyme featured in the invention with an isolatedAdx polypeptide, an isolated AdR polypeptide and a substrate selectedfrom the group consisting of polycyclic and unsaturated mono alcoholshaving an aliphatic side chain such as cholesterol, a cholesterolanalogue and a cholesterol derivative in conditions allowing thetransformation of said substrate into a steroid hormone precursor, and

b) recovering the steroid hormone precursor obtained.

As used herein, the term “substrate” encompasses polycyclic andunsaturated mono alcohols having an aliphatic side chain such asphytosterol derivated from cycloartenol and lanosterol. Among thesesubstrates, “cholesterol, cholesterol analogues and derivatives thereof”refers to a list of substrates selected from the group consisting ofcholesterol, brassicasterol, campesterol, ergostadienol such as ergosta5, 22 dienol, ergosta 5, 24 (28) dienol, ergosta 5, 24(28) diene 3betaol, ergosta 5, 24 (25) dienol, ergostatrienol such as ergosta 5, 22, 24(25) trienol, ergosta 5, 22, 24 (28) trienol, ergosta 5, 7, 22 trienol,ergostatetrenol such as ergosta 5, 7, 22, 24 (25) ou ergosta 5, 7, 22,24 (28), desmosterol, beta-sitosterol, generol, a mixture of oxysterols,stigmasterol, vitamin D, 7-Dehydrocholesterol and ergosterol. Sterolmixes currently used in industrial processes are also encompassed inthis definition of substrates, such as generol 100 and ADM90 (comprisingbrassicasterol+campesterol+stigmasterol+beta-sitosterol at differentratios).

In a particular embodiment, the substrate is selected from the groupconsisting of cholesterol, campesterol, desmosterol and ergosta 5,24(28) diene 3beta ol. In a specific embodiment, the substrate isergosterol.

In a specific embodiment, the “steroid hormone precursor” is selectedfrom the group consisting of pregnenolone, 7-Dehydropregnenolone,Hydroxyergosterol, and Hydroxystigmasterol. In another specificembodiment, said steroid hormone precursor is selected from the group ofhydroxylated cholesterol analogues and secosteroids (such as vitamins D2and D3 as derivatives of the cholesterol analogues 7-dehydrocholesteroland ergosterol). In a particular embodiment, the steroid hormoneprecursor is pregnenolone.

“Culturing the microorganism in the presence of a substrate” meansphysically interacting said microorganism with a substrate as definedabove. This interaction can be achieved within a culture medium or not.In a specific embodiment, said culture medium contains agents for thepermeabilization of a microorganism according to the present inventionand/or the solubilization of a substrate according to the presentinvention. Dissolution of the substrate in these agents can be prior tothe addition to microorganism culture.

“Contacting a P450 enzyme with a substrate” means physically interactingsaid P450 enzyme with a substrate as defined above. This interaction canbe achieved within a medium or not. In a specific embodiment, saidmedium contains agents for the solubilization of a substrate accordingto the present invention. Dissolution of the substrate in these agentscan be prior to the addition to said medium.

The agents used for the dissolution of the substrate can be selectedfrom the group consisting of ethanol, Tween-80, tergitol,polyvinylpyrrolidone (PVP), saponins (such as Quillaja saponin which iscontained within crude extracts of the soap bark tree Quillaja saponariafor example), cyclodextrins and derivatives thereof (e.g.2-hydroxypropyl-β-cyclodextrin). In another specific embodiment,mixtures of these agents can be used, such as a mixture of ethanol andTween-80, a mixture of tergitol and ethanol, a mixture of saponins (e.g.Quillaja saponin) and cyclodextrins as non-limiting examples.Cyclodextrin derivatives can be used, such as2-hydroxypropyl-β-cyclodextrin. In another specific embodiment,substrates are co-crystallized with polyvinylpyrrolidone (PVP).

In another embodiment, substrate is first dissolved in2-hydroxypropyl-β-cyclodextrin prior to addition to the microorganismculture wherein said culture contains Quillaja saponin. In anotherembodiment, substrates are dissolved in a solution comprising apercentage of 2-hydroxypropyl-β-cyclodextrin ranging from 10 to 60%,e.g., 20 to 50%, e.g., 40 to 50%, and a percentage of Quillaja saponinranging from 1 to 10%, e.g., 2 to 8%, e.g., 3 to 6%. In anotherembodiment, substrates are dissolved in a solution comprising 45% of2-hydroxypropyl-β-cyclodextrin and 4% of Quillaja saponin.

In another embodiment, the final concentration of2-hydroxypropyl-β-cyclodextrin in the microorganism culture is between 1and 4%, e.g., between 2 and 3%, such as 2.25% as illustrated in example2. In another embodiment, the final concentration of Quillaja saponin inthe microorganism culture is between 0.05 and 0.25%, e.g., between 0.075and 0.225%, e.g., between 0.1 and 0.2%.

The “culturing of said microorganism under conditions allowing theexpression of said exogenous nucleic acid sequences” may be performedaccording to any well-known culturing and inducing methods in thebiotechnology field such as described in Bleif et al. (Appl MicrobiolBiotechnol (2012) 93:1135-1146) or in Korneli et al. (Journal ofBiotechnology 163 (2013) 87-96).

“Conditions allowing the transformation of said substrate into a steroidhormone precursor” include in vitro conditions, such as the reagentsused, the reagent concentrations, the temperature, the use of agitation,the duration of the reaction or incubation, etc., which favors thetransformation of said substrate into a steroid hormone precursor. Theseconditions may be determined and adjusted by methods known to thoseskilled in the art.

As a non-limiting example, the reaction may be performed in presence ofglucose-6-phosphate dehydrogenase and glucose-6-phosphate, typically in150 mM of HEPES buffer, for example adjusted to pH 7.4, containingtypically 0.05% Tween-20 and 1 mM MgCl2. The concentrations of the P450enzyme, Adx and AdR may for instance be of 1 μM, 20 μM and 0.5 μM, or of0.25 μM, 5 μM and 0.125 μM, respectively. The polycyclic and unsaturatedmono alcohols having an aliphatic side chain such as cholesterol,cholesterol analogue or cholesterol derivative may be dissolved in 45%2-hydroxypropyl-β-cyclodextrin. The samples may be pre-warmed to 37° C.and NADPH may be added to a final concentration of 100 μM. The mixturesmay be incubated at 37° C. with agitation.

In a specific embodiment, the steroid hormone precursor used in anymethod for producing a steroid hormone precursor is pregnenolone. Asused herein, “pregnenolone” refers to a steroid hormone also referred toas 3β-hydroxypregn-5-en-20-one.

BRIEF DESCRIPTION OF THE SEQUENCES

SEQ ID NO: 1 shows the amino acid sequence of CYP11A1 comprising athreonine at position 225 and an aspartic acid at position 289(polypeptide SA1).

SEQ ID NO: 2 shows the amino acid sequence of CYP11A1 comprising athreonine at position 225.

SEQ ID NO: 3 shows the amino acid sequence of CYP11A1 comprising anaspartic acid, at position 289.

SEQ ID NO: 4 shows the amino acid sequence of WT Bos taurus CYP11A1(polypeptide SA4; WT P450scc).

SEQ ID NO: 5 shows the sequence of the plasmid pSMF2.1_CYP11A1BYMencoding for SA1 of SEQ ID NO: 1.

SEQ ID NO: 6 shows the amino acid sequence of the polypeptide SA6(P450scc-I1A-K193E).

SEQ ID NO: 7 shows the amino acid sequence of AdR.

SEQ ID NO: 8 shows the amino acid sequence of Adx.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: HPLC-chromatogram showing the in vitro conversion of 20 μMcholesterol by the cytochrome P450 polypeptides SA1 (SEQ ID NO:1) andSA4 (control having sequence SEQ ID NO: 4). Legend: S: substrate, P:main product, DOC: 11-deoxycorticosterone.

FIG. 2: Pregnelonone quantification from HPLC-chromatogram showing thein vivo conversion of different substrates into pregnenolone by thecytochrome P450 polypeptide SA1 (SEQ ID NO:1).

FIG. 3: HPLC-chromatogram showing the in vivo conversion of 300 μMcholesterol by the cytochrome P450 polypeptides SA1 (SEQ ID NO:1) andSA6 (control having sequence SEQ ID NO: 6) after 24 h. Legend: Chol.:cholesterol, Prog.: pregnenolone.

FIG. 4: Time course for the in vivo conversion of 300 μM cholesterol bythe cytochrome P450 polypeptides SA1 (SEQ ID NO:1) and SA6 (controlhaving sequence SEQ ID NO: 6).

FIG. 5: Vector map of pSMF2.1_CYP11A1BYM encoding for SA1 (SEQ ID NO:1).

EXAMPLES Example 1 Materials and Methods

Protein Synthesis

CYP11A1 variants were obtained by gene synthesis and cloned intopTRC99A, fused to a poly-His tag. C43DE3-E. coli cells wereco-transformed with each vector and the chaperone-encoding pGro12. Thepurification was performed as described in Janocha et al. (BiochimBiophys Acta. (2011) January;1814(1):126-31). The purity was assessed bySDS-PAGE. Concentrations of the purified proteins were determined byCO-difference spectra, after treatment with sodium dithionite andexposure to CO.

Adx and AdR were purified according to Uhlmann et al. (Biochem. Biophys.Res. Commun., 188 (1992), pp. 1131-1138) and Sagara et al. (Biol. Pharm.Bull., 16 (1993), pp. 627-630), respectively.

In Vitro Conversion Assay

For in vitro enzyme assays, 150 mM of HEPES buffer, adjusted to pH 7.4,containing 0.05% Tween-20 and 1 mM MgCl2, were applied as reactionbuffer. 1 unit of glucose-6-phosphate dehydrogenase, with 5 mMglucose-6-phosphate as substrate, served as a NADPH-regenerating system.

For WT P450scc (noted “SA4”, SEQ ID NO: 4) and P450scc-I1A-K193E (noted“SA6”, SEQ ID NO: 6) the concentrations of CYP11A1, Adx and AdR were of1 μM, 20 μM and 0.5 μM, and for P450scc-R225T-N289D (noted “SA1”, SEQ IDNO: 1) the concentrations of CYP11A1, Adx and AdR were of 0.25 μM, 5 μMand 0.125 μM, respectively.

20 μM of cholesterol, dissolved in 45% 2-hydroxypropyl-β-cyclodextrin,served as substrate for CYP11A1.

The samples were pre-warmed to 37° C. and the reaction was started byaddition of NADPH to a final concentration of 100 μM. The mixtures wereincubated at 37° C. with agitation for 30 s. The reaction was stopped byboiling the samples in water for 30 s.

To allow photometric detection at 240 nm, the steroids were convertedinto their 3-keto-Δ4 derivatives using a cholesterol oxidase fromNocardia spec.

20 μl of a cholesterol oxidase solution (5 mg cholesterol oxidase and 5mg Na-cholate dissolved in 5 ml of 50 mM HEPES buffer pH 7, containing0.05% Tween-20) were added to the samples. After incubation at 37° C.for 1 h, 11-deoxycorticosterone (DOC) was added to the reaction mixturesas an internal standard, followed by a 2-times extraction with equalvolumes of ethylacetate. After evaporation, the extracts were dissolvedin acetonitrile/water.

In Vivo Conversion Assay

The in vivo conversion of 300 μM cholesterol into pregnelonone wasevaluated by HPLC after 24 h. Bacillus megaterium was cultivated inTB-medium containing 10 μg/ml tetracycline at 37° C. with 180 rpmshaking. Protein expression was induced by adding 0.25 g of xylosedissolved in 1 mL water, followed by the subsequent addition of thesubstrate, dissolved in 2-hydroxypropyl-β-cyclodextrin.

Example 2 In Vitro Conversion of Cholesterol by the Cytochrome P450Polypeptides SA1 (SEQ ID NO:1) and SA4 (WT Control, SEQ ID NO:4)

After acute evaluation of the concentration of each P450scc preparation,SA1, SA4 and SA6 were used in the following in vitro assays. Each ofthese isoforms was reconstituted at a concentration of 1 μM in thepresence of cholesterol as a substrate (20 μM) in saturating amounts ofAdx and AdR.

While SA4 and SA6 showed identical activity, SA1 showed a 2-3-foldhigher activity compared to SA4 and SA6 (FIG. 1). Since the substrate isalready depleted after the incubation time, it is difficult to assessthe differences between the SA1 and SA1/SA4 polypeptides at longerincubation time.

Example 3 In Vivo Conversion of Cholesterol by the Cytochrome P450Polypeptides SA1 (SEQ ID NO:1) and SA6 (Control, SEQ ID NO:6)

As no measurable differences were observed between SA4 and SA6, theinventors focused their interest on comparing the SA1 and SA6polypeptides. A new system was recently developed in which cholesterolis metabolized into pregnenolone by recombinant Bacillus megateriumexpressing P450scc, Fdx1 and FdxR in the presence of solubilizedcholesterol. SA1 and SA6 corresponding cDNAs were optimized for Bacillusmegaterium codon BIAS and transferred into the plasmid pSFM2.1 using theappropriate restriction sites. Both PSFM2.1 plasmids bearingrespectively the codon optimized SA1 and SA6 were transferred intoBacillus megaterium MS941 using a classical protoplast transformationprotocol.

The in vivo cholesterol conversion activity was assessed after 24 h and48 h for the SA1 and SA6 polypeptides expressed in Bacillus megaterium.

In accordance with the in vitro experiments, SA1 exhibited now a 2-foldhigher activity compared to SA6 (FIGS. 3 and 4).

Example 4 In Vivo Conversion of Different Substrates into Pregnenoloneby the Cytochrome P450 Polypeptide SA1 (SEQ ID NO:1)

Finally the improved system was used to test the SA1 polypeptideconversion capacity with various substrates of biotechnologicalinterest: campesterol, desmosterol, ergosta-5,24(28)-dien-3β-ol and amixture of various 20, 22-OH oxysterols.

Each substrate was converted to one main product with the same retentiontime as progesterone, indicating that CYP11A1 was able to cleave theside-chain of each of these substrates, yielding pregnenolone.

Pregnenolone formation was quantified for every substrate (FIG. 2). Thepolar oxysterols were converted at a rate comparable to cholesterol (˜35mg/L after 48 hours). Conversion of the more hydrophobic sterolscampesterol, desmosterol and ergostadienol only occurred at a rate ofapproximately 19% after 48 hours, compared to cholesterol.

Taken together, the results show that all of the tested steroids wereable to permeate through the cell membrane of Bacillus megaterium andwere converted to pregnenolone by the CYP11A1 SA1 mutant.

The inventors thus report here a new P450scc protein, named SA1, whichshows an increased conversion activity towards various sterols includingcholesterol.

1. An isolated P450 enzyme comprising an amino acid sequence at least80% identical to SEQ ID NO: 1, wherein said sequence comprises one orboth of a threonine at a position corresponding to position 225 and anaspartic acid at a position corresponding to position
 289. 2. The enzymeaccording to claim 1 comprising a sequence selected from the groupconsisting of SEQ ID NO: 1, SEQ ID NO: 2 and SEQ ID NO:
 3. 3. The enzymeaccording to claim 1, consisting of the sequence SEQ ID NO:
 1. 4. Anisolated nucleic acid comprising a nucleotide sequence encoding anenzyme as defined in claim
 1. 5. A vector comprising a nucleic acidcomprising a nucleotide sequence encoding a P450 enzyme, wherein theenzyme comprises an amino acid sequence at least 80% identical to SEQ IDNO: 1, wherein said amino acid sequence comprises one or both of athreonine at a position corresponding to position 225 and an asparticacid at a position corresponding to position 289, and wherein thenucleotide sequence is operatively associated with an expression controlsequence.
 6. The vector according to claim 5, further comprising one ormore of a nucleic acid sequence encoding adrenodoxin (Adx) and a nucleicacid sequence encoding adrenodoxin reductase (AdR).
 7. A host cellcomprising a vector that comprises a nucleic acid comprising anucleotide sequence encoding a P450 enzyme, wherein the enzyme comprisesan amino acid sequence at least 80% identical to SEQ ID NO: 1, whereinsaid amino acid sequence comprises one or both of a threonine at aposition corresponding to position 225 and an aspartic acid at aposition corresponding to position 289, and wherein the nucleotidesequence is operatively associated with an expression control sequence.8. The host cell according to claim 7, wherein the host cell is agenetically engineered microorganism.
 9. The host cell according toclaim 7, wherein the host cell is Saccharomyces cerevisiae.
 10. Agenetically engineered microorganism capable of converting a substrateselected from the group consisting of polycyclic and unsaturated monoalcohols having an aliphatic side chain such as cholesterol, acholesterol analogue and a cholesterol derivative, into a steroidhormone precursor, wherein said microorganism comprises a nucleic acid,comprising a nucleotide sequence encoding an enzyme as defined inclaim
 1. 11. An in vitro method for preparing an enzyme as defined inclaim 1, said method comprising the steps of: a) culturing a host cellcomprising a vector that comprises a nucleic acid comprising anucleotide sequence encoding a P450 enzyme, wherein the enzyme comprisesan amino acid sequence at least 80% identical to SEQ ID NO: 1, whereinsaid amino acid sequence comprises one or both of a threonine at aposition corresponding to position 225 and an aspartic acid at aposition corresponding to position 289, and wherein the nucleotidesequence is operatively associated with an expression control sequence,wherein the host cell is cultured under conditions suitable to obtainexpression of the enzyme; and b) recovering the expressed enzyme. 12.(canceled)
 13. A method for producing a steroid hormone precursor,comprising the steps of: a) providing a microorganism comprising thevector of claim 5, b) culturing said microorganism under conditionsallowing the expression of the P450, c) contacting the microorganismculture obtained at step b) with a substrate selected from the groupconsisting of polycyclic and unsaturated mono alcohols having analiphatic side chain such as cholesterol, a cholesterol analogue and acholesterol derivative, in conditions allowing the production, by themicroorganism, of a steroid hormone precursor from said substrate, andd) recovering the steroid hormone precursor produced.
 14. A method forproducing a steroid hormone precursor, comprising the steps of: a)contacting the P450 enzyme of claim 1 with an isolated adrenodoxin (Adx)polypeptide, an isolated adrenodoxin reductase (AdR) polypeptide and asubstrate selected from the group consisting of polycyclic andunsaturated mono alcohols having an aliphatic side chain such ascholesterol, a cholesterol analogue and a cholesterol derivative inconditions allowing the transformation of said substrate into a steroidhormone precursor, and b) recovering the steroid hormone precursor. 15.The method according to claim 13, wherein the steroid hormone precursoris pregnenolone.
 16. The method according to claim 14, wherein thesteroid hormone precursor is pregnenolone.